Rubio talks to reporters in June after a closed door briefing on Capitol Hill.

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Photos:Moments from Marco Rubio's career

Rubio speaks to the media in front of a wall dedicated to the victims of the violence in Venezuela as he shows support for the Venezuelan community at a restaurant in Doral, Florida, in April 2014.

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Photos:Moments from Marco Rubio's career

Rubio speaks to the media at the Doral restaurant in April 2014.

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Photos:Moments from Marco Rubio's career

Rubio checks his phone in March as he arrives for a Capitol Hill news conference to introduce a proposal for an overhaul of the tax code.

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Photos:Moments from Marco Rubio's career

Rubio, left, is greeted as he arrives at a restaurant in Doral in February 2014.

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Photos:Moments from Marco Rubio's career

Rubio, left, and Florida Gov. Rick Scott speak to the media in Doral in February 2014.

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Photos:Moments from Marco Rubio's career

From left, Sens. Cory Booker, Rubio, Kristen Gillibrand and John McCain wait for Obama to deliver the State of the Union address in January 2014.

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Photos:Moments from Marco Rubio's career

Rubio addresses an event held by the American Enterprise Institute for Public Policy Research in January 2014.

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Photos:Moments from Marco Rubio's career

Paralympian Brad Snyder poses with Rubio during a Team USA Congressional visit in November 2013.

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Photos:Moments from Marco Rubio's career

Rubio speaks in November 2013 during a campaign stop for Virginia Attorney General Ken Cuccinelli, the Republican candidate for governor of Virginia.

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Photos:Moments from Marco Rubio's career

Rubio confers with McCain as U.S. Ambassador to Syria Robert Ford testifies before the Senate Foreign Relations Committee in October 2013.

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Photos:Moments from Marco Rubio's career

Rubio, center, speaks to members of the media as Sen. Ron Johnson, left, and Rep. Ron DeSantis listen during a news conference on Capitol Hill in October 2013.

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Photos:Moments from Marco Rubio's career

Rubio returns to the Capitol after meeting with Obama and other Republican leaders about the government shutdown in October 2013.

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Photos:Moments from Marco Rubio's career

Rubio speaks to an aide on Capitol Hill as he arrives for the weekly Senate Republican Policy Committee luncheon in September 2013.

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Washington (CNN)The nonprofit group backing Florida Sen. Marco Rubio's bid for the White House has raised nearly $16 million, the organization announced Monday.

The Conservative Solutions Project, which as a tax-exempt organization is not required to disclose its donors, said those contributors have given them $15.8 million. The super PAC associated with that nonprofit -- Conservative Solutions PAC, which must name its backers and their donations -- will have to release its totals by the end of the month.

Though political nonprofits can shield the names of their donors, they are limited in the amount of money they can spend advocating for the election or defeat of candidates. The group's first television advertisement praised Rubio's leadership on negotiations with Iran, but did not directly call for him to win the GOP nomination.

The nonprofit group said Monday that it would boost the size of that advertising campaign to $3.3 million, having spent $1 million in its first week. The organization said it has now raised two-thirds of the money it hopes to over the course of the campaign.

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Allies of other candidates, like Jeb Bush, have recently set up similar nonprofit organizations to bolster their political operations, while some other Republican rivals used their older groups to serve as de facto campaigns prior to their kickoff events.